This invention relates to an anchoring device for use in reconstructing torn ligament connections, such as the anterior cruciate ligament (ACL) in the knee. Specifically, this invention relates to an improved fixation screw, called an intra-articular tendon sling fixation screw by the inventor, which is formed as a unitary construct. The fixation screw has a threaded shank portion that can be inserted into bone and a head portion formed with an eyelet through which a graft, such as an autograft, an allograft or a prosthetic ligament, can be looped.
The fixation screw of the present invention is particularly suited for reconstructive surgery in which the fixation screw is preferably inserted completely into bone and directly receives the graft. As such, the present invention is particularly suited for ACL reconstruction and for posterior cruciate ligament (PCL) reconstruction in the knee. It is to be noted that ACL reconstruction has become a common operation. On the other hand, PCL reconstruction surgery is performed much less often as significant knee function can be maintained without the benefit of the PCL. Thus, for illustrative purposes, this specification will focus on ACL reconstruction surgery to illustrate the use, function and benefits of the present invention.
Reconstructive surgeries of the ACL date back as far as 1904. Since that time, a variety of different methods and devices for aiding in the reconstruction of the ACL have been patented and described. Most modern techniques utilize arthroscopic procedures to minimize the size of any incisions made. U.S. Pat. No. 5,374,269, granted to Thomas D. Rosenberg on Dec. 20, 1994 (hereinafter referred to as Rosenberg '269) is illustrative of the prior art. Rosenberg '269 describes variations on a number of common techniques of ACL reconstruction.
Rosenberg '269 specifically claims a method of forming a passageway in a femur at the knee joint. Its specification does not limit itself, however, to only describing this specific sub-procedure. Rosenberg '269 describes two ACL reconstruction methods that use the patellar tendon as the graft and one method that uses the semitendinosus tendon. Both the patellar tendon and the semitendinosus tendon can be harvested from the individual having the knee surgery and are, therefore, autografts. These tendons are commonly used as the replacement graft for the torn or ruptured ACL. In each of the methods described in Rosenberg '269, tunnels are drilled in the tibia and the femur. These tunnels end in the intra-articular space of the joint at the attachment sites of the torn or ruptured ACL. The tunnel in the tibia goes from the tibial cortex at a site between 20 and 25 mm below the knee joint to the intra-articular space of the knee joint. The tunnel in the femur is a closed-end tunnel, although it may be formed with a channel that extends to the lateral surface of the femur, depending on the graft attachment method used. Rosenberg '269 modifies the prior art method of drilling the femoral tunnel, but is otherwise indicative of an accepted practice for forming the femoral and tibial tunnels.
In Rosenberg '269, the graft, whether a patellar tendon or a semitendinosus tendon, is implanted with one end secured in the closed-end femoral tunnel and the other end secured in the tibial tunnel or at a point adjacent to the tibial tunnel on the tibial cortex.
In the first method described by Rosenberg '269, using the patellar tendon, the bone plug on the leading end of the graft can be locked in place in the femoral tunnel with an interference screw. Rosenberg '269 also teaches a method by which the leading end bone plug is attached with sutures that are anchored to the lateral femoral cortex by means of a button. The sutures pass through a channel that extends from the closed end of the femoral tunnel to the lateral surface of the femur. The sutures attach to the leading bone plug. In both methods using the patellar tendon, the trailing bone plug is secured by staples to the tibial cortex below the tibial tunnel entrance.
Rosenberg '269 also describes a method for anchoring the semitendinosus tendon. Elongated sutures are attached to the ends of the semitendinosus tendon graft. The leading end of the graft is secured in a manner similar to the second method for securing the patellar tendon in the femoral tunnel described above. That is by means of sutures attached to a button on the lateral femur cortex, which are passed through a channel to the end of the femoral tunnel where they attach to the semitendinosus graft. The trailing edge of the graft is secured in the tibial tunnel by means of sutures that are affixed to a screw or post positioned on the tibia adjacent to the entrance of the tibial tunnel.
While the methods of preparing tunnels in the bones of the knee joint taught by Rosenberg '269 are applicable to methods using the present invention, the present device differs materially from any device taught in Rosenberg '269. The fixation screw of the present invention is an anchor. Rosenberg '269 teaches an interference screw. Furthermore, use of the fixation screw of the present invention requires vastly differing attachment methods for grafts than the methods taught by Rosenberg '269. First, the inventor prefers not to use the patellar tendon as a graft for ACL reconstruction. Second, when the fixation screw of the present invention is used with the semitendinosus tendon, there is no need to form a channel from the closed-end tunnel in the femur to the surface of the femoral cortex, nor is there a need to make a lateral incision at the lateral femoral cortex as is necessary with the method described by Rosenberg '269. Thus, methods employing the present invention reduce the number of incisions made and trauma to the femur or other bone in which the fixation screw is inserted. They also do not require the use of sutures for anchoring the leading end of the semitendinosus tendon in the femoral tunnel.
While the present invention differs from the devices and methods taught by Rosenberg '269 in both form and use, two endosteal ligament retaining devices have been described that are more similar to the present invention in the methods by which they anchor a graft in the femur. They are U.S. Pat. No. 5,129,902, entitled "Endosteal Ligament Retainer," granted to E. Marlowe Goble and Karl Somers on Jul. 14, 1992 (hereinafter referred to as Goble '902) and U.S. Pat. No. 5,152,790, entitled "Ligament Reconstruction Graft Anchor Apparatus," granted to Thomas D. Rosenberg, Gerard S. Carlozzi and William J. Reimels on Oct. 6, 1992 (hereinafter referred to as Rosenberg '790). Like the present invention, these inventions teach an anchor inserted into a closed-end femoral tunnel that receives a graft. Also like the present invention, both of these devices are used in methods where the closed-end femoral tunnel is formed in the femur in a fashion similar to Rosenberg '269. However, like the method for which the present invention is designed and unlike Rosenberg '269, these methods and devices do not need a channel formed in the femur that passes from the closed-end tunnel to the lateral femoral cortex. Goble '902 teaches an anchor consisting of a basket or disk for receiving a graft which is rotatably attached to a screw. The graft receiving disk or basket is able to spin on the screw head, preventing the graft from twisting or rotating as the screw is driven into the closed end of the femoral tunnel. The graft can either be looped through an opening in the basket or sutured to the basket.
Rosenberg '790 also teaches an anchor assembly consisting of a basket, called a ring in this case, for receiving the graft which is rotatably attached to a threaded body member. Like Goble '902, the graft receiving basket is able to spin on the threaded body member. Rosenberg '790, however, teaches suturing the graft to the ring.
There are a number of material differences between the prior art and the present invention. Both Goble '902 and Rosenberg '790 are multi-component anchors having moving parts. This can lead to complications. Furthermore, because the diameter of the basket of Goble '902 is much larger than the threads of the fixation screw, it could become wedged against the edge or side of the femoral tunnel during installation, making it difficult to fully insert or retrieve the anchor. It is to be noted that both Goble '902 and Rosenberg '790 teach using sutures as an intermediate means for attaching the graft to the anchor. The sutures are the weak link in the attachment and suture breakage is a consideration. Also, neither of the prior art devices are cannulated for use with a guide drill. Finally, in both Goble '902 and Rosenberg '790, because the means for attachment of the graft are located away from the central axis of the anchor or threaded member, the graft cannot be aligned with the axis of the anchor member, either during or after installation.
Furthermore, in Goble '902, when sutures are not used to attach the graft to the basket, the graft can end up being pinched between the basket and the wall of the femoral tunnel. This is because the graft or grafts must loop through openings in the arcuate walls of the basket on its periphery.
To summarize, the present invention provides a fixation screw that has no moving parts, that can be installed in a closed-end femoral tunnel with the use of a guide drill, receive a graft without the necessity of sutures, receive a graft without causing pinching of the graft between the fixation screw and the wall of the femoral tunnel, and that allows the anchored graft to be aligned with the central axis of the fixation screw.